1. Field of the Invention
The present invention relates to an optical subscriber network system, and more particularly, an optical subscriber network system that supports broadcast and communication services using a fiber to the home (FTTH) network.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional optical subscriber network. As shown in FIG. 1, an optical subscriber network system providing broadcast/communication service includes an optical line terminal (hereinafter, referred to as an OLT), an optical network unit (hereinafter, referred to as an ONU), and an optical cable. The OLT converts broadcast data transmitted from a broadcaster into an optical signal to provide a user with broadcast service. It then transmits one tied optical signal. The ONU is a user-side apparatus and transmits information, which is received from the OLT, to a subscriber. The optical cable connects the OLT to the ONU. Operationally, the ONU receives a service requirement from a terminal of a service user. The ONU then provides a corresponding service. The broadcast/communication data, which is transmitted from the broadcaster, is transmitted to the ONU via the OLT,
In such an optical subscriber network system, when an optical signal is transmitted to a home, signals such as continuous Ethernet broadcast signals or video on demand (VOD) signals are transmitted to a subscriber in a single direction. A burst Ethernet communication signal is burst when it is transceived. Such directionality and continuity makes it difficult to transmit the two signals together. Therefore, broadcast signals in various channels are multiplexed by time division multiplexing (TDM). Then one optical wavelength is assigned to the multiplexed signal by a coarse wavelength division multiplexing (hereinafter, referred to as a CWDM). In this way, another optical wavelength is assigned to the Ethernet communication signal by the CWDM. By using such a CWDM method, a fiber to the home (FTTH) network is realized.
Shown in FIG. 2 is a conventional FTTH optical subscriber network system, in which a bi-directional transceiving of a digital broadcasting and an Internet signal is possible. Such a network includes a server-side bi-directional optical transmitter 110 (hereinafter, referred to as an OLT) and a subscriber-side bi-directional optical receiver 120 (hereinafter, referred to as an ONU). The OLT 110 includes a first laser diode (hereinafter, referred to as a LD) 111 for transmitting digital broadcast data, a second LD 112 for transmitting downstream Internet data, a server-side photo diode (hereinafter, referred to as a PD) 113 for receiving upstream Internet data, a band-pass filter 114 which is installed in front of the server-side PD 113 and passes only the upstream Internet data, and an multiple optical waveguide element 115 for dividing each input/output data. The ONU 120 includes an multiple optical waveguide element 125 for dividing data inputted from the server-side bi-directional optical transmitter 110, a first PD 121 for receiving the digital broadcast data inputted from the server-side bi-directional optical transmitter 110, a second PD 122 for receiving the downstream Internet data inputted from the server-side bi-directional optical transmitter 110, and a subscriber-side LD 123 for transmitting upstream Internet data.
The server-side PD 113 detects upstream Internet data 127 input from the subscriber-side. It enables a server computer to recognize the upstream Internet data 127. The first LD 111 is a vertical cavity surface emitting laser (hereinafter, referred to as a VCSEL). The VCSEL modulates input digital broadcast data 116 into an optical signal and transmits the modulated optical signal the ONU 120. The second LD 112 is a VCSEL having a wavelength different from the first LD 111. The second LD 112 modulates downstream Internet data 117 into an optical signal and transmits the modulated optical signal the ONU 120.
In addition, the subscriber-side LD modulates the upstream Internet data 127. This data is transmitted from the subscriber-side to the server-side. The subscriber-side LD modulates this data into an optical signal and outputs it. Further, the subscriber-side LD forms a pair with the second PD 122 in the subscriber-side and enables bi-directional transceiving of an Internet signal. The first PD 121 detects and outputs the digital broadcast data 116 modulated into an optical signal by the first LD 111. The second PD 122 detects the downstream Internet data 117 transmitted from the second LD 112 and converts it into data that can be recognized by a computer in the subscriber-side.
However, since such a conventional FTTH optical subscriber network system requires two optical signals (i.e. an optical signal for transmitting an image signal and an optical signal for transmitting an communication signal) the OLT 100 must transmit signals through the two LD 111 and 112. It also requires an optical coupler, which is an optical waveguide element, for coupling the signals. Accordingly, the system manufacturing cost increases. Further, even when the two signals are received in the ONU 200, the ONU 200 needs a coupler, which is an optical waveguide element, for dividing the two signals and the two PD 121 and 122. Thus, the number of parts and the system manufacturing cost are increased.